Project Summary A group of eight major users seek funding for the acquisition of Electron Paramagnetic Resonance (EPR) equipment to modernize an existing spectrometer. The requested equipment will enable operation in the Q-band frequency range (34 GHz) along with microwave pulse shaping. Together, these capabilities will provide a modern and flexible platform for performing high-quality Double Electron-Electron Resonance (DEER) spectroscopy for determining long distances, and resolving complex distance distributions, in proteins and protein assemblies. The instrument to be upgraded was originally installed in 1989, and has long served laboratories at UC Santa Cruz and around the San Francisco Bay Area, providing a wealth of biomedical advances. However, due to its age, this instrument is now unreliable and obsolete, compared to modern instruments, and not capable of performing the high sensitivity experiments required by the NIH-funded major users. The requested upgrade will retain the existing magnet and high- power X-band (9.4 GHz) amplifier, but will replace the console, microwave bridge and low- temperature cryostat, along with addition of high-power Q-band components. The specific EPR configuration will greatly facilitate throughput and efficiency, enabling a range of critically needed EPR capabilities. This modernized instrument will play a central role in diverse, NIH- funded research programs, with direct impact on neurodegenerative diseases, biological clock assemblies, complex membrane transporters, proteins that regulate immune responses and calcium binding proteins involved in vision.